Seat weight measuring apparatus

ABSTRACT

A seat weight measuring apparatus includes a support body one end of which is fixed in position relative to a vehicle body and the other end of which is displaced corresponding to a load from a vehicle seat side. The apparatus includes a permanent magnet which is disposed at one end of the support body and a held body which has a shape retaining property and is held by the other end of the support body, and a detector which is disposed on a tip of the held body to face the permanent magnet with a space therebetween.

BACKGROUND

The present invention relates to a seat weight measuring apparatus, installed to a vehicle seat, for measuring a weight corresponding to body weight of an occupant.

Seat occupancy detecting apparatuses installed to vehicle seats are well known in the art. Such a seat occupancy detecting apparatus provides information about occupancy of a vehicle seat. The information is used for a detection switch for determining whether or not a seat belt is fastened, for example, by detecting the insertion of a seat belt tongue to a seat belt buckle, whereby the detection switch can operate in conjunction with the information about occupancy.

The seat occupancy detecting apparatus detects occupancy according to ON/OFF of switches installed in seat slide rails or a seat cushion of the vehicle seat. When the occupancy is detected and the seat belt is not fastened, an alarm for promoting an occupant to fasten the seat belt is provided, for example, by turning on an indicator lamp.

On the other hand, recently, there has been a demand for actuating an airbag to control an inflator to set a developing volume of the airbag into a plurality of levels or a demand to set a belt tension of a seat belt into a plurality of levels.

This is attributed to demands to make the pressure for developing the airbag or the belt tension of the seat belt to differ between an adult and a child.

A seat occupancy detecting apparatus which detects only occupancy as mentioned above does not enable such a control as to set the developing volume of an airbag by controlling the actuation of the airbag into a plurality of levels or set the belt tension of a seat belt into a plurality of levels.

FIGS. 9(A), 9(B) show an example of a seat weight measuring apparatus which detects at least a plurality of levels of a weight of an occupant sitting in a seat so as to enable such a control as to set the developing volume of an airbag into a plurality of levels or set the belt tension of a seat belt into a plurality of levels (for example, see Japanese Patent Unexamined Publication 2003-329519, hereby incorporated by reference herein in its entirety). FIG. 9(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 9(B) is a cross sectional view of a weight sensing section thereof.

In FIGS. 9(A), 9(B), the seat weight measuring apparatus 1 is provided with a support body 4 fixed to a seat rail 2 by a nut 3.

The support body 4 is provided with a fixing shaft 4 a which is chamfered to correspond to the shape of an opening 2 a formed in the seat rail 2 so as to limit the rotation in radial directions and which is substantially oval in section. The fixing shaft 4 a projects from one end of the support body 4. The fixing shaft 4 a is formed in its outer periphery with thread groove whereby the nut 3 is screwed onto the fixing shaft 4 a. The support body 4 is also provided on the other end with a projection 4 c having a cable through hole 4 b formed therein. Further, the support body 4 is formed with a concave portion 4 d having a cylindrical section and a hollow portion 4 e providing a hollow space between the cable through hole 4 c and the concave portion 4 d. The support body 4 except the fixing shaft 4 a, i.e. the other end side portion of the support body 4, is surrounded by a surrounding portion 5 a formed in an arm 5 with keeping away from the surrounding portion 5 a, the arm 5 composing a part of a vehicle seat body (the entire body is not shown). The projection 4 c is fitted in an opening 5 b formed in the surrounding portion 5 a. Held in the cable through hole 4 b is an end of a resin cylindrical collar 6 having a shape retaining property. In the hollow portion 4 e, an inner wall is composed of rounded curved walls in order to reduce stress concentration (notch effect) caused when a load (weight) by a seating force F is applied. For example, the rounded curved walls are formed by milling operation.

A cable 7 for transmitting detected signals is passed through the cylindrical collar 6. On one end of the cable 7, a detector 8 facing the concave portion 4 d is provided.

As shown in FIG. 9(B), in the normal state, the detector 8 is positioned substantially coaxially with the concave portion 4 d and is substantially equally spaced apart from the inner wall of the concave portion 4 d. The detector 8 comprises a permanent magnet (magnetism generating device) 8A on the tip thereof and a magnetic sensor (magnetism detecting device) 8B which is Hall IC. In the normal state, the permanent magnet 8A and the sensor 8B are positioned coaxially with the concave portion 4 d. That is, the axis of magnetic field of the permanent magnet 8A extends along the axis of the support body 4.

In the structure as mentioned above, when the vehicle seat body is occupied by an occupant, a seating force F corresponding to the weight of the occupant to be measured is transmitted to the projection 4 c of the support body 4 through the arm 5. As a result, the support body 4 is deformed because the support body 4 is supported at one side in the seat rail 2 just like a cantilever. The deformation amount is measured from displacement direction and displacement amount of the detector 8 relative to the concave portion 4 d, thereby measuring the weight of the occupant.

That is, even when the support body 4 having the hollow portion 4 e is deformed, the cylindrical collar 7 is not deformed without being affected by the deformation of the support body 4. Therefore, the axis of the cylindrical collar 7 is inclined relative to the axis of the support body 4 so that the relative position between the detector 8 and the concave portion 4 d is varied. As for lines of magnetic flux of the permanent magnet 8A composing the outer periphery of the detector 8, the strength of magnetic field is increased at a region where the distance in the radial direction is narrower. The variation in strength of magnetic field is detected by the sensor 8B, thereby measuring the weight of the occupant.

The deformation of the support body by the seating force F depends on the distance between supported portions, that is, the distance between the opening 2 a of the seat rail 2 and the opening 5 b of the arm 5.

By the way, in the seat weight measuring apparatus having the aforementioned structure, the concave portion 4 d is positioned all around the periphery of 360° of the detector 8.

The detection accuracy of the detector 8 must depend on the load during the fixing operation (for example, the force of screwing the nut 3) when the detector 8 is installed to the vehicle seat so that it is required to take such load into consideration. In addition, the permanent magnet 8A may be displaced in the horizontal direction (the direction shown by leftward and rightward arrows ← → in FIG. 9(B)) of the vehicle by load due to twisting given when the seat is installed to the vehicle, thus resulting in error of measurement.

Accordingly, it is quite difficult to arrange the axis of the detector 8 coaxially with the axis of the concave portion 4 d. There are further problems that irregularity of alignment may be one of factors causing error of measurement as mentioned above and the alignment requires skill. Moreover, there is another problem of increasing the assembly cost because confirmation and adjustment operation for the measurement accuracy are required.

SUMMARY

It is an object of the present invention to provide a seat weight measuring apparatus capable of maintaining sufficient measurement accuracy without setting excessive measurement accuracy, capable of preventing error of measurement, and capable of simplifying the structure and thus preventing the assembly cost from being increased.

A seat weight measuring apparatus according to an embodiment of the present invention comprises: a support body one end of which is fixed in position relative to a vehicle body and the other end of which is displaced corresponding to a load from a vehicle seat side; a held body which has a shape retaining property and is held at its middle position by the other end of said support body; a held body facing portion for detecting displacement of said support body which is formed in said support body to face a tip of said held body such that a distance from the tip of said held body to the held body facing portion in the vertical direction of a vehicle body is smaller than a distance from the tip of said held body from the held body facing portion in the horizontal direction; and a magnetism detecting device disposed on the tip of said held body, wherein load from the vehicle seat side is measured based on variation in strength of magnetic field accompanying variation in distance between said held body facing portion and the tip of said held body in the vertical direction, said variation being linked with displacement of said support body corresponding to the load from the vehicle seat side.

A seat weight measuring apparatus according to another embodiment of the present invention can have said held body facing portion comprising a first magnetism generating device, and said magnetism detecting device detects the strength of magnetic filed which is generated from said first magnetism generating device and varies depending on said distance in said vertical direction of the vehicle body.

A seat weight measuring apparatus according to another embodiment includes said first magnetism generating device being disposed over the held body only at the upper side of the vehicle body.

A seat weight measuring apparatus according to another embodiment further comprises a second magnetism generating device disposed on the tip of said held body, wherein said magnetism detecting device detects the strength of magnetic filed which is generated from said second magnetism generating device and varies depending on said distance in said vertical direction of the vehicle body.

A seat weight measuring apparatus in another embodiment includes said held body facing portion having a structure with an opening on at least one side in said horizontal direction of the vehicle body.

A seat weight measuring apparatus in another embodiment comprises: a support body in which the rigidity in the vertical direction of a vehicle body is set to be smaller than the rigidity in the horizontal direction of the vehicle body, and one end of which is fixed in position relative to a vehicle body and the other end of which is displaced corresponding to a load from a vehicle seat side, a held body which has a shape retaining property and is held at its middle position by the other end side of said support body, a held body facing portion for detecting displacement of said support body which is formed in said support body to face a tip of said held body, and a magnetism detecting device disposed on the tip of said held body, wherein load from the vehicle seat side is measured based on variation in strength of magnetic field accompanying variation in distance between said held body facing portion and the tip of said held body, said variation being linked with displacement of said support body corresponding to the load from the vehicle seat side.

A seat weight measuring apparatus according to another embodiment includes said held body facing portion comprising a third magnetism generating device, and said magnetism detecting device detects the strength of magnetic filed which is generated from said third magnetism generating device and varies depending on said distance.

A seat weight measuring apparatus according to yet another embodiment further comprises a fourth magnetism generating device disposed on the tip of said held body, wherein said magnetism detecting device detects the strength of magnetic filed which is generated from said fourth magnetism generating device and varies depending on said distance.

The seat weight measuring apparatus of an embodiment of the present invention is capable of maintaining sufficient measurement accuracy without setting excessive measurement accuracy, capable of preventing error of measurement, and capable of simplifying the structure and thus preventing the assembly cost from being increased.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.

FIGS. 1(A), 1(B) show an example 1 of the seat weight measuring apparatus of the present invention, wherein FIG. 1(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 1(B) is a cross sectional view of a weight detecting section thereof.

FIG. 2 shows an embodiment of the seat weight measuring apparatus of the present invention and is a perspective view of main parts of the seat weight measuring apparatus.

FIGS. 3(A), 3(B) show a variation of the embodiment of the seat weight measuring apparatus of the present invention, wherein FIG. 3(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 3(B) is a cross sectional view of a weight detecting section thereof.

FIGS. 4(A), 4(B) show a variation of the embodiment of the seat weight measuring apparatus of the present invention, wherein FIG. 4(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 4(B) is a cross sectional view of a weight detecting section thereof.

FIGS. 5(A), 5(B) show a variation of the embodiment of the seat weight measuring apparatus of the present invention, wherein FIG. 5(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 5(B) is a cross sectional view of a weight detecting section thereof.

FIGS. 6(A), 6(B) show another variation of the embodiment of the seat weight measuring apparatus of the present invention, wherein FIG. 6(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 6(B) is a cross sectional view of a weight detecting section thereof.

FIGS. 7(A), 7(B) show another embodiment of the seat weight measuring apparatus of the present invention, wherein FIG. 7(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 7(B) is a cross sectional view of a weight detecting section thereof.

FIG. 8 shows the seat weight measuring apparatus of that of FIGS. 7(A) and 7(B) and is a perspective view of main parts of the seat weight measuring apparatus.

FIGS. 9(A), 9(B) show a conventional seat weight measuring apparatus, wherein FIG. 9(A) is a longitudinal sectional view of the seat weight measuring apparatus and FIG. 9(B) is a cross sectional view of a weight detecting section thereof.

DETAILED DESCRIPTION

Hereinafter, the seat weight measuring apparatus of the present invention will be described with reference to drawings.

FIGS. 1(A), 1(B) and FIG. 2 show an example 1 of the seat weight measuring apparatus of the present invention, wherein FIG. 1(A) is a longitudinal sectional view of the seat weight measuring apparatus FIG. 1(B) is a cross sectional view of a weight detecting section thereof, and FIG. 2 is a perspective view of main parts of the seat weight measuring apparatus.

In these drawings, the seat weight measuring apparatus 11 comprises a support body 14 fixed to a seat rail 12 via a nut 3 and a housing 15 surrounding the support body 14.

The support body 14 is provided with a fixing shaft 14 a which is chamfered to correspond to the shape of an opening 12 a formed in the seat rail 12 so as to limit the rotation in radial directions and which is substantially oval in section. The fixing shaft 14 a projects from one end of the support body 14. The fixing shaft 14 a is formed in its outer periphery with thread groove, whereby the nut 13 is screwed onto the fixing shaft 14 a. The support body 14 is also provided on the other end with a projection 14 c having a cable through hole 14 b formed therein. Further, the support body 14 is formed with a concave portion 14 d (held body facing portion) extending along a horizontal axis perpendicular to the axis of the support body 14 (in the depth direction as seen in FIG. 1(A) and FIG. 2) and a hollow portion 14 e providing a hollow space between the cable through hole 14 c and the concave portion 14 d. In the hollow portion 14 e, an inner wall is composed of rounded curved walls in order to reduce stress concentration (notch effect) caused when a load (weight) by a seating force F is applied. For example, the rounded curved walls are formed by milling operation.

The housing 15 is fixed to an arm 16 composing a part of a vehicle seat body (the entire body is not shown) by a nut 17. The housing 15 surrounds the support body 14 except the fixing shaft 14 a, i.e. the other end side portion of the support body 14, with keeping away from the support body 14. The housing 15 holds the projection 14 c by the opening 15 a thereof.

A cable (held body) 18 having a shape retaining property is held at its middle position by the cable through hole 14 b. A detector 20 is disposed on a tip of the cable 18 such that the detector 20 faces a magnetism generating device (a permanent magnet in this example, the same is true of the following) 19 of which section is a U-like shape opening to the cable through hole 14 c and which is disposed in the concave portion 14 d.

As shown in FIG. 1(B), the permanent magnet 19 faces the detector 20 at a predetermined distance in the vertical direction of the vehicle body and opens in the horizontal direction of the vehicle body. It should be noted that the permanent magnet 19 does not necessarily open in the horizontal direction. It is enough to satisfy such a condition that the distance between the permanent magnet 19 and the detector 20 in the horizontal direction is sufficiently longer the distance between the permanent magnet 19 and the detector 20 in the vertical direction.

The detector 20 has a magnetic sensor (magnetism detecting device) inside thereof and the sensor is Hall IC. In the normal state, the detector 20 is positioned at the middle in the vertical direction relative to the permanent magnet 19.

In the structure as mentioned above, when the vehicle seat body is occupied by an occupant, a seating force F corresponding to the weight of the occupant to be measured is transmitted to the projection 14 c of the support body 14 through the arm 16 and the housing 15. As a result, the support body 14 is deformed because the support body 14 is supported at one side in the seat rail 12 just like a cantilever. The deformation amount is measured from displacement amount of the permanent magnet 19 relative to the detector 20, thereby measuring the weight of the occupant.

That is, as the support body 14 is deformed, the cable 18 is inclined about the cable through hole 14 b so as to vary the relative position between the detector 20 and the permanent magnet 19. As for the lines of magnetic flux of the permanent magnet 19, the strength of magnetic field is increased at a region where the distance between the detector 20 and the permanent magnet 19 is narrower. The variation in strength of magnetic field is detected by the sensor of the detector 20, thereby measuring the weight of the occupant.

Since the permanent magnet 19 opens in the horizontal direction, the detector 20 has detection range only in the vertical direction of the vehicle body, thereby preventing error of measurement due to accidental displacement in the horizontal direction of the vehicle body.

By the way, since it is enough for measuring the weight that the displacement when the detector 20 displaces in the upward direction of the vehicle body is detected by the detector 20, the permanent magnet 29 may be disposed only at the upper side of the vehicle body as shown in FIGS. 3(A), 3(B) and FIGS. 4(A), 4(B). Alternatively, the permanent magnet 19 may be buried in the support body as shown in FIGS. 5(A), 5(B).

As another variation, as shown in FIGS. 6(A), 6(B), both a permanent magnet 19 and a detector 20 are disposed on the tip of the cable 18 and a sensor within the detector 20 detects a variation in strength of magnetic field corresponding to variation in vertical distance between the detector 20 and a concave portion 14 d as a held body facing portion. In these cases, the same effect can be obtained.

FIGS. 7(A), 7(B) and FIG. 8 show an example 2 of the seat weight measuring apparatus of the present invention, wherein FIG. 7(A) is a longitudinal sectional view of the seat weight measuring apparatus, FIG. 7(B) is a cross sectional view of a weight detecting section thereof, and FIG. 8 is a perspective view of main parts of the seat weight measuring apparatus.

In these drawings, the seat weight measuring apparatus 21 comprises a support body 14 fixed to a seat rail 12 via a nut 13 and a housing 15 surrounding the support body 14.

The support body 14 is a block construction comprising end parts 14A, 14B, an upper surface part 14C and a lower surface part 14D each having a substantially flat plate shape (the end parts 14A, 14B and the surface parts 14C, 14D are fixed by suitable fixing device such as welding or rivets). According to the side opening structure, the support body 14 is designed such that the rigidity in the vertical direction of the vehicle body is smaller than the rigidity in the horizontal direction of the vehicle body.

The end part 14A of the support body 14 is provided with a fixing shaft 14 a which is chamfered to correspond to the shape of an opening 12 a formed in the seat rail 12 so as to limit the rotation in radial directions and which is substantially oval in section. The fixing shaft 14 a projects from one end of the end part 14A. The fixing shaft 14 a is formed in its outer periphery with thread groove, whereby the nut 13 is screwed onto the fixing shaft 14 a. The end part 14B of the support body 14 is also provided on the other end with a projection 14 c having a cable through hole 14 b formed therein. Further, the support body 14 is formed with a concave portion 14 d (held body facing portion) extending along a horizontal axis perpendicular to the axis of the support body 14 (in the depth direction as seen in FIG. 7(A) and FIG. 8) and with a hollow portion 14 e providing a hollow space between the end part 14A and the end part 14B of the support body 14.

Since the housing 15 has substantially the same structure as that in example 1, the detail description of the housing 15 will be omitted.

On the other hand, a cable 18 having a shape retaining property is held at its middle position by the cable through hole 14 b of the support body end part 14B. A detector 20 is disposed on a tip of the cable 18 such that the detector 20 faces a magnetism generating device (a permanent magnet in this example, the same is true of the following) 19 of which section is a U-like shape opening to the cable through hole 14 c and which is disposed in the concave portion 14 d.

In the same manner as the example 1, the distance between the permanent magnet 19 and the detector 20 in the horizontal direction of the vehicle body is set to be sufficiently longer than the distance between the permanent magnet 19 and the detector 20 in the vertical direction of the vehicle body. The details of the detector 20 are also the same as the aforementioned example 1.

In the structure of the example 2 as mentioned above, when the vehicle seat body is occupied by an occupant, a seating force F corresponding to the weight of the occupant to be measured is transmitted to the projection 14 c of the support body end part 14B similarly to the aforementioned example 1. As a result, the support body 14 is deformed because the support body 14 is supported at one side in the seat rail 12 just like a cantilever. The deformation amount is measured from displacement amount in relative position between the permanent magnet 19 and the detector 20, thereby measuring the weight of the occupant.

That is, as the support body 14 is deformed, the cable 18 is inclined about the cable through hole 14 b so as to vary the relative position between the detector 20 and the permanent magnet 19 because the position of the support body end part 14A is fixed relative to the seat rail 12. As for the lines of magnetic flux of the permanent magnet 19, the strength of magnetic field is increased at a region where the distance between the detector 20 and the permanent magnet 19 is narrower. The variation in strength of magnetic field is detected by the sensor of the detector 20, thereby measuring the weight of the occupant.

Since the support body 14 is designed such that the rigidity in the vertical direction of the vehicle body is smaller than the rigidity in the horizontal direction of the vehicle body, the support body 14 is easily deformed (deflected) particularly in the vertical direction. In addition, the permanent magnet 19 opens in the horizontal direction and the detector 20 has detection range only in the vertical direction of the vehicle body. These prevent error of measurement due to accidental displacement in the horizontal direction of the vehicle body. This example also provides another effect of facilitating the workability of the support body 14 because of the block construction mentioned above.

In the aforementioned example 2, in so far as the effect by the present invention of improving the detection accuracy in the vertical direction of the vehicle body as compared to the conventional art is obtained, the distance between the permanent magnet 19 and the detector 20 in the horizontal direction of the vehicle body may be set to be the same as that in the vertical direction of the vehicle body, besides that the permanent magnet 19 is formed to open in the horizontal direction of the vehicle body and that the distance between the permanent magnet 19 and the detector 20 in the vertical direction of the vehicle body may be set to be smaller that in the horizontal direction of the vehicle body. In this case, because of the difference in rigidity of the support body 14, the detection accuracy in the vertical direction of the vehicle body is improved at least from the conventional art.

Also in the aforementioned example 2, similarly to the aforementioned variation shown in FIGS. 6(A), 6(B), both the permanent magnet 19 and the detector 20 may be disposed on the tip of the cable 18 so that a sensor within the detector 20 detects a variation in strength of magnetic field corresponding to variation in vertical distance between the detector 20 and a concave portion 14 d as a held body facing portion. In these cases, the same effect can be obtained.

The priority document, Japanese Application No. 2004-154153, filed May 25, 2004, including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.

Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims. 

1. A seat weight measuring apparatus comprising: a support body one end of which is fixed in position relative to a vehicle body and the other end of which is configured to be displaced in response to a load from a vehicle seat side; a held body which has a shape retaining property and is connected to the other end of the support body; wherein the support body includes a held body facing portion that faces a tip of the held body such that a distance from the tip of the held body to the held body facing portion in the vertical direction of a vehicle body is smaller than a distance from the tip of the held body to the held body facing portion in the horizontal direction; and wherein a magnetism detecting device is disposed on the tip of the held body, wherein load from the vehicle seat side is measured by detecting a variation in the strength of a magnetic field detected by the magnetism detecting device, wherein the variation results from the displacement of the support body corresponding to the load from the vehicle seat side.
 2. The seat weight measuring apparatus according to claim 1, wherein the held body comprises a cable.
 3. The seat weight measuring apparatus according to claim 1, wherein the held body facing portion comprises a first magnetism generating device, and the magnetism detecting device is configured to detect the strength of magnetic field which is generated from the first magnetism generating device and varies depending on the distance in the vertical direction of the vehicle body.
 4. The seat weight measuring apparatus according to claim 3, wherein the first magnetism generating device comprises a permanent magnet.
 5. The seat weight measuring apparatus according to claim 3, wherein the first magnetism generating device is disposed over the held body only at the upper side of the vehicle body.
 6. The seat weight measuring apparatus according to claim 1, further comprising a second magnetism generating device disposed on the tip of the held body, wherein the magnetism detecting device detects the strength of magnetic field which is generated from the second magnetism generating device and varies depending on the distance in the vertical direction of the vehicle body.
 7. The seat weight measuring apparatus according to claim 1, wherein the held body facing portion has a structure with an opening on at least one side in the horizontal direction of the vehicle body.
 8. A seat weight measuring apparatus comprising: a support body, wherein the rigidity of the support body in the vertical direction of a vehicle body is less than the rigidity of the support body in the horizontal direction, and wherein one end of the support body is fixed relative to the vehicle body and the other end of the support body is configured to be displaced in response to a load from a vehicle seat side; a held body which has a shape retaining property and is connected to the other end side of the support body; a held body facing portion for detecting displacement of the support body which is formed in the support body to face a tip of the held body; and a magnetism detecting device disposed on the tip of the held body, wherein load from the vehicle seat side is measured based on variation in strength of magnetic field resulting from a variation in the distance between the held body facing portion and the tip of the held body, the variation corresponding to displacement of the support body resulting from the load from the vehicle seat side.
 9. The seat weight measuring apparatus according to claim 8, wherein the held body facing portion comprises a third magnetism generating device, and wherein the magnetism detecting device detects the strength of magnetic field which is generated from the third magnetism generating device and varies depending on the distance.
 10. The seat weight measuring apparatus according to claim 8, further comprising a fourth magnetism generating device disposed on the tip of the held body, wherein the magnetism detecting device detects the strength of magnetic field which is generated from the fourth magnetism generating device and varies depending on the distance.
 11. A seat weight measuring apparatus comprising: a support body one end of which is fixed in position relative to a vehicle body and the other end of which is displaced corresponding to a load from a vehicle seat side; a cable held at its middle position by the other end of the support body; a cable facing portion for detecting displacement of the support body which is formed in the support body to face a tip of the cable, the cable facing portion comprising a permanent magnet; and a magnetic detector disposed on the tip of the cable, wherein the magnetic detector has a detection range only in the vertical direction.
 12. The seat weight measuring apparatus according to claim 11, wherein the permanent magnet is open in the horizontal direction.
 13. The seat weight measuring apparatus according to claim 11, wherein the distance between the permanent magnet and the magnetic detector in the horizontal direction is larger than the distance between the permanent magnet and the magnetic detector in the vertical direction.
 14. The seat weight measuring apparatus according to claim 11, wherein load from a vehicle seat side is measured based on variation in strength of magnetic field accompanying variation in distance between the cable facing portion and a tip of the cable. 